Recent developments and applications of protective silicone coatings: A review of PDMS functional materials

The classification of silicones in the literature is as broad as their properties and applications; in this work, we have restricted the discussion to polydimethylsiloxanes. Silicones, classified here as derivatives of polydimethylsiloxane (PDMS), are organically modified inorganic-type macromolecules of silicon with different molecular weights, sizes and chemical properties. The presence of the organic and inorganic components within these copolymers/oligomers/polymers accounts for their multi-phased chemistries since either covalent or ionic linkages connect their hybrid molecular chains. As ceramers derived via sol-gel type routes, some products of silicone syntheses result in functional materials with both physical and chemical properties intermediate between normal polymers and pristine ceramics. Hybrid materials of this kind form very stable chemical bonds on surfaces. The strong chemical bonding inherent within their siloxane (-Si-O-) networks as well as their thermal stability promote inertness against chemical attack, hence, their potential as protective coatings. Products of silicone chemistry are normally applied as films on metal substrates in multi-layered patterns aimed at protecting these surfaces from environmental influences. In this work, several classes of protective coatings synthesized from a wide range of PDMS derivatives have been enlisted and discussed comparatively in terms of their barrier properties. The ease of modifications of these compounds in order to attain improved barrier properties have also been highlighted. More highlights on coating applications with functional materials incorporated with small molecules as well as those whose molecular chains are terminated with reactive organofunctional chemical groups, are also presented. This work is an attempt to comply protective applications of surface and pretreatment films made from PDMS, covering areas of anticorrosion, anti-biofouling, anti-icing, flame-resistance, self-cleaning as well as anti-reflection. The reasons for their unique protective abilities have been addressed for every chosen application, and the influences of precursor chemistries on the physical and chemical properties of resultant functional coating materials have also been discussed. This work also features polydimethylsiloxanes as potential risk of hazardous substances (RoHS) compliant additives in industrial coatings, and as reliable alternatives for chromate/tributyltin-loaded barrier films deployed in the field.